How do I fix frequent crashes on iMac?

There is a world of difference between those two reports. In the first one in March, your hard drive is practically dead. The one from today is within expectations for that Fusion configuration. THe File System scores, an indicator of drive health, is horrible ("timed out"), but in today's showing excellent health.

What happened between the two tests?

Mar 26 drive scores:

Performance:

System Load: 2.73 (1 min ago) 2.37 (5 min ago) 1.16 (15 min ago)

Nominal I/O usage: 70.45 MB/s

File system: 122.02 seconds (timed out) 😱

Write speed: 34 MB/s 😱

Read speed: 82 MB/s 😱

April 15 drive scores:

Performance:

System Load: 2.39 (1 min ago) 2.58 (5 min ago) 1.43 (15 min ago)

Nominal I/O usage: 17.34 MB/s

File system: 24.25 seconds 👍🏻

Write speed: 609 MB/s 👍🏻

Read speed: 1361 MB/s 👍🏻

Please see this user tip: EtreCheck: How to download EtreCheck, run… - Apple Community

It will explain how to download and use etrecheck to generate a report that can be used to help us help you troubleshoot the problem.

Failing hard drive - This computer has a hard drive that appears to be failing.

The KP implicates that suspicion. It should not have been difficult for your Local Mac support to have reached that conclusion quickly.

The iMac appears to be OK...

The problem is MS software overload.

Is the RAM installed original, or did you upgrade it at some point.

My first guess would be incompatible, marginal, or bad RAM.

Good eye Allan.

I think that John was looking at the OP's first report and I was looking at the OP's second report.

I would still like to know if the RAM is original or aftermarket.

I've seen too many bizarre crashes with aftermarket RAM to dismiss that as a possibility.

👍